From polarization entanglement to color entanglement

Youhei Okawa, Fuminori Omura, Yuhsuke Yasutake +1 more

Girish Ashok Kulkarni, Anand K. Jha

Zhihui Yan, Xiaojun Jia

The direct generation of discrete-variable three-photon polarization entanglement has been recently demonstrated [Nat. Photonics8, 801 (2014)10.1038/nphoton.2014.218NPAHBY1749-4885]. Here, we propose a feasible scheme to generate continuous-variable (CV) three-color polarization entangled states of light in a deterministic way. The method initially prepares a tripartite quadrature entanglement based on two cascaded nondegenerate optical parametric oscillators. The entangled modes are then coupled, respectively, with three strong coherent optical beams on polarized beam splitters, leading to the generation of the three-color CV polarization entanglement. The polarization entanglement is then verified by inseparability criterion and positive partial transposition criterion. Additionally, optimal parameters in practical conditions are obtained through numerical simulations, which could provide useful guidance for experimental implementations. The demonstrated CV three-color polarization entanglement is suitable in quantum information processing tasks relying on the direct interaction between spin of atoms and polarization of light.

Sanjit Karmakar, Ronald E. Meyers

This article proposes a polarized entangled photon source in optical fiber with low Raman noise that features the controllable generation of specific signal and idler wavelengths (colors) by varying the pump power. The novel two color source can provide needed telecom entangled photon wavelengths for applications in quantum communications, quantum computing, and quantum imaging.

Natalia Korolkova

Sven Ramelow, Lothar Ratschbacher, Alessandro Fedrizzi +2 more

Although frequency multiplexing of information has revolutionized the field of classical communications, the color degree of freedom (DOF) has been used relatively little for quantum applications. We experimentally demonstrate a new hybrid quantum gate that transfers polarization entanglement of nondegenerate photons onto the color DOF. We create, for the first time, high-quality, discretely color-entangled states (with energy band gap up to 8.4 THz) without any spectrally selective filtering, and unambiguously verify and quantify the amount of entanglement (tangle, 0.611 +/- 0.009) by reconstructing a restricted density matrix; we generate a range of maximally entangled states, including a set of mutually unbiased bases for an encoded qubit space. The technique can be generalized to transfer polarization entanglement onto other photonic DOFs, like orbital angular momentum.